A mouse is a computer input device used for positioning a cursor on a computer video display. A typical embodiment of a mouse includes an enclosure that lies flat on a work space, one or more user-actuated switches or buttons located externally of the enclosure, X and Y motion sensors, electrical interface circuitry, and a cable to connect the mouse to a host computer and video display. The switches, often in the form of push buttons, enable alteration of the program flow in the host computer. In operation, when the user moves the mouse on a flat surface, the motion sensors sense the movement in the directions of the X and Y planes. The interface circuitry, typically located within the mouse enclosure, converts the raw movement and switch information into digital information, which is supplied to the host computer. Software in the host computer uses the motion and switch information to perform different functions, for example, repositioning the cursor on the computer display screen.
Mice of the above described type are normally classified by the manner in which the motion is detected, the principal motion detection methods being mechanical and optical. Mechanical mice usually employ a technique whereby a spherical ball protrudes slightly below the bottom of the mouse enclosure and is free to roll as the user along a flat and level drawing surface moves the mouse. Inside the enclosure, the rolling ball is coupled to a pair of orthogonally mounted shaft position encoders. The mechanical mouse motion is thereby converted by the encoders into two pairs of quadrature signals, one pair for each axis of motion, thereby providing the required direction and displacement information corresponding to the mouse movement.
The mechanical mouse requires that both the ball and the enclosure be in contact with the drawing surface. This limits the mechanical mouse to use on an essentially level surface so that the ball is held against the drawing surface by gravity. In addition, due to the limits at which the ball can travel in and out of the enclosure, it will not function properly, if at all, on curved surfaces. Another limitation of the mechanical mouse is that when in the process of lifting the mouse or when pressing the mouse into a soft surface, the orthogonally mounted encoding shafts detect a ball position change with respect to the enclosure, false position data can be sent to the host computer. A further limitation is that oil, grease, hair, or dirt can cause the ball to become stuck or to not rotate freely again causing false position data to be sent to the host.
Optical mice utilize a light source in the base of the mouse enclosure, light therefrom being reflected onto one or more photodetectors from a specifically patterned grid surface over which the mouse is moved. Typically, a single chip computer translates the changes in detected luminance into direction and displacement information, which is utilized by the host computer in the manner described above. Like mechanical mice, an optical mouse requires an essentially flat level surface in order to provide proper focus.
Other input devices are used in electronic devices. For portable devices, input devices that can be controlled by a finger are preferred. Trackpads are input devices that have flat surfaces and detect finger movement by either resistive or capacitive sensing technologies. Trackballs are essentially upside down mice thereby allowing the user to use a finger to rotate the ball. While trackballs are well liked by users, the limitations of the optical mice also apply and often the ball becomes stuck and does not rotate freely causing poor cursor positioning. Trackpoints™ are pressure sensing pointing devices that use the force exerted by a finger to direct movement. While the small size of the trackpoint is beneficial in some products, users complain about the difficulty in finding the correct force to apply and the trackpoint's tendency to drift. Therefore, there is a need for an ergonomic input device technology that is reliable.